Project summary At every instant of our lives, a cacophony of sounds impinges on our ears and challenges our brain to make sense of the complex acoustic environment in which we live ? a phenomenon referred to as the cocktail party problem (CPP). Up till now, efforts to understand this phenomenon focused on the role of acoustic cues in shaping sensory encoding of auditory objects in the brain. Yet, listening is not the same as hearing. It engages both sensory and cognitive processes to enable the brain to adapt its computational primitives and neural encoding to the changing soundscape and shifting demands to attend to various sounds in the scene. The current proposal puts forth an adaptive theory of auditory perception which integrates the role of both sensory mechanisms and cognitive control in a unified multiscale theory that combines neural processes at the level of single neurons, neural populations and across brain areas. Central to this hypothesis is the role of rapid neural plasticity that reshapes brain responses to acoustic stimuli according to the statistical structure of the soundscape, guided by feedback mechanisms from memory and attention. The research plan translates this hypothesis into a unified multiscale model employing a distributed inference architecture (Aim 1). This scheme employs hierarchical dynamical systems that track the statistical structure of the stimulus at different resolutions and time-scales, and adapt their responses based on both memory and attentional priors. This architecture is used as springboard to predict the interaction between sensory and cognitive mechanisms at play during the CPP. It also affords a general solution to the scene analysis problem that will be interfaced with existing sound technologies (e.g. speech recognition, medical diagnosis, target tracking and surveillance). This computational effort is informed and validated with empirical data (Aim 2) from experiments in human subjects, using psychoacoustics and EEG; as well as single-unit electrophysiology in behaving ferrets. The experiments shed light of neural processes underlying the CPP using rich stimuli that manipulate the statistical structure as well as attentional focus of subjects (humans/animals). The final integrated theory is refined in perceptual studies in young and aging adults whose perception is highly challenged by complex listening soundscapes (Aim 3). This effort generates testable predictions about failures in auditory perception in multisource environments especially in aging adults and pinpoints possible malfunctions due to sensory or cognitive factors. By shedding light on the functional principles and neural underpinnings underlying the sensory and cognitive interaction during the CPP, the research will have a big impact on our understanding of auditory perception in cluttered scenes. In addition, it has direct relevance to health and wellbeing, particularly for improving communication aids for the sensory impaired and aging populations; as well as affording adaptive processing to sound technologies (e.g. speech recognition, audio analytics) which remain for the most part static and hard-wired. 1